When a wireline 911 call is initiated, the call is directed to an assigned local Public Safety Answering Point (PSAP). The PSAP answers the call and receives an inbound telephone number or Automatic Number Identification (ANI) information. This number is used to query an Automatic Location Identification (ALI) database, match it with the corresponding address as a location of the calling party, and forward the location information and inbound telephone number to the assigned PSAP. The PSAP can deliver both the number and the location to the appropriate emergency service (e.g., fire, police and/or ambulance) for dispatch.
The above scenario works well when the 911 call originates from a wireline device (e.g., a wireline phone at a residence) because every wireline number is associated with a unique, static address. For mobile devices, such as mobile phones, however, the location changes as the mobile subscriber travels to different locations. Accordingly, the FCC has mandated the use of a technology known as enhanced 911 (E911) to enable mobile devices to process 911 emergency calls and enable emergency services to determine the location of the calling party.
Prior to 1996, wireless 911 callers would have to access their service providers to get verification of subscription service before the call could be routed to a PSAP. In 1996, the FCC ruled that a 911 call must be routed directly to the PSAP without receiving verification of service from a specific mobile operator. The FCC further mandated that the call must be handled by any available carrier even if the carrier is not the calling party's home carrier. Under the FCC's rules, all mobile phones manufactured for sale in the United States after Feb. 13, 2000 must be able to operate in analog mode and must include this special method for processing 911 calls.
The FCC has proposed a phased rollout of E911. In 1998, Phase I was implemented and required that mobile operators identify the originating phone number and the location of the base station or cell within a 1 mile accuracy. Phase I E911 rules require a 7, 8 or 10 digit number to accompany each 911 call. The number provides a callback number for the PSAP dispatcher to use if the call is disconnected or otherwise compromised.
In 2001, Phase II was implemented and required that each mobile operator in the United States offer handset- or network-based location detection capability so that the calling party's location is determined by the geographic location of the mobile handset within 100 meter accuracy. The FCC refers to this as Automatic Location Identification (ALI). Phase II E911 rules provide a more accurate location for the dispatcher to use.